Generally, an ACF is a connecting material applied to the case that members can not be connected to each other by a soldering method as the members are made of special materials or have fine pitch signal wirings.
The ACF is typically used to package LCD panels, printed circuit boards (PCBs), driver IC circuits and so on in LCD modules.
For example, an LCD module has a plurality of driver ICs mounted thereon for driving thin film transistor (TFT) patterns. A method for mounting a driver IC on an LCD module mainly includes a chip on glass (COG) mounting method for mounting a driver IC on a gate area and a data area of an LCD panel without an additional structure, and a tape automated bonding (TAB) mounting method for indirectly mounting a driver IC on a gate area and a data area of an LCD panel through a tape carrier package (TCP) having the driver IC mounted thereon.
However, electrodes of the driver IC and electrodes of the LCD panel are arranged at fine pitches, and thus any mounting method has a difficulty in using a means such as soldering. For this reason, the ACF is generally used in electrically connecting the electrodes of the driver IC to the electrodes of the LCD panel.
FIG. 1 is a plane view of an LCD module using a typical TAB method, and FIG. 2 is a cross-sectional view taken along the line II-II′ of FIG. 1. Referring to FIGS. 1 and 2, a PCB 10 is located in a row direction of an LCD panel 20 as a source for transmitting external signals to the LCD panel 20, and a TCP 30 having a drive IC 31 mounted thereon electrically connects the LCD panel 20 to the PCB 10. At this time, the ACF 40 is used in electrically connecting the LCD panel 20 to the TCP 30 and the TCP 30 to the PCB 10.
The ACF 40 includes an insulating adhesive and conductive particles dispersed in the insulating adhesive, and when the ACF 40 is interposed between the members and is compressed using heat, the conductive particles between opposite terminals come in contact with each other, and thus the opposite terminals are electrically connected to each other. At this time, insulation is sustained at an x-y plane and electrical connection is established in a z-axis direction. More specifically, referring to FIG. 2 taken along the line II-II′ of FIG. 1, the ACF 40 is interposed between the TCP 30 and the PCB 10, which includes an insulating adhesive composition 41 and a plurality of conductive particles 42 dispersed in the insulating adhesive composition 41. Subsequently, when the anisotropic conductive film 40 is compressed using predetermined temperature and pressure, the conductive particles 42 interposed between electrodes 32 of the TCP 30 and electrodes 14 of the PCB 10 electrically connects the opposite electrodes 32 and 14. This connecting method is also applied to electrical connection between the TCP 30 and the LCD panel 20 in the same manner.
Meanwhile, it is general to observe cracks or pressed state of the conductive particles 42 using a microscope so as to check an electrical connection state of the members connected by the anisotropic conductive film 40.
However, this method requires a separate inspection step, thereby delaying a process, and has a limitation of inspecting only a restricted portion of a sample. And, because at least one substrate should have a transparent property to observe the pressed state of the conductive particles, the method has a limitation in wide application.